Various types of equipment which can be used by a person for performing aerobic exercises have become very popular over the past decade or so. There are many designs of aerobic exercise equipment on the market, including Universal of Nautilus exercising machines, stationary bicycles, and leg and arm exercising equipment. A type of aerobic exercise apparatus which has become particularly popular is an apparatus which simulates climbing stairs. There are many designs of simulated stair exercisers on the market, available for a wide range of prices. An elaborate stair simulator is sold under the trade-mark STAIRMASTER. This apparatus has among other things a computerized program by which the resistance provided by the simulated stairs can be varied. This device is expensive and is not portable. Furthermore, the STAIRMASTER apparatus must remain erect at all times.
U.S. Pat. No. 304,358, Timothy O. Armstrong et al., assigned to Precor Incorporated, illustrates a stair climbing exercise apparatus which is constructed of a base, a handle, left and right foot levers, and hydraulic cylinders which provide adjustable resistance for the foot levers. A difficulty with this apparatus is that the foot pedals, since they are part of levers which are pivoted about a common fulcrum, do not remain level. Accordingly, the exerciser's feet do not remain horizontal while performing the simulated stair climbing exercise. Further, the apparatus cannot be collapsed into a compact position for storage.
U.S. Pat. No. 5,013,031, J. W. Bull, illustrates an exercise apparatus which comprises a support structure, a left foot lever pivotally connected to the support structure and a right foot lever pivotally connected to the support structure. A rotatable shaft is also rotatably attached to the support structure. A first clutch means is drivingly connected to the rotatable shaft. The first clutch means independently drives the rotatable shaft in a first-rotational direction when the first clutch means is rotated in the first-rotational direction. The first clutch means overrrides the rotatable shaft when the first clutch means is rotated in the counter first-rotational direction. A second clutch means is also drivingly connected to the rotatable shaft. The second clutch means independently drives the rotatable shaft in the first-rotational direction when the second clutch means is rotated in the first rotational direction.
This exercise apparatus suffers from the deficiency that the left foot lever and the right foot lever do not remain horizontal throughout their travel from an upper position to a lower position and vice versa. Accordingly, the exerciser's feet do not remain level throughout the exercise cycle, which would be the case if the exerciser were actually climbing a set of stairs. Also, the apparatus is not collapsible.